This invention relates generally to axial flow rotary separators for combines of the type used for harvesting and treating grain crops and the like and more particularly to threshing bars for the rotors of such separators.
The general mode of operation of such combines and their separators is well known, as is the difficulty of feeding harvested crop material smoothly and efficiently into the threshing section where the threshing action depends on relatively small radial clearances between the rotor, and particularly its threshing bars, and the separator casing, and particularly its threshing grate or concave portions.
Typically a combine is equipped with a header which gathers crop material and delivers it by means of a feeder conveyor rearwards and upwards to the infeed portion of the separator. There the crop material enters a forward portion of the separator casing to be engaged by a rotor infeed portion which begins the transformation of the received generally linear flow of crop material into an annular mat spiraling rearward to enter the threshing portion of the separator, preferably smoothly and uniformly. Means such as helical guide elements on the inside of the housing or angled material moving blades on the rotor are provided to maintain the rearwardly spiraling movement of the crop material. This transformation of a generally diffuse mass of material delivered by the feeder conveyor into an attenuated mat thin enough to enter the threshing zone is particularly difficult in tough harvesting conditions, such as in high-moisture crops with long straw. Inevitably, portions of the material arrive at the inlet to the threshing zone in bunches or ropes consuming extra power and placing extra loads on the threshing bars as the material is made to conform to the physical limitations of the threshing zone inlet.
Attempts to better condition received crop material for entry into the threshing zone have included modification of the material control and conveying elements of the feed rotor itself and, as described in copending U.S. patent application Ser. No. 889,626, provision of a transition rotor portion, between feed rotor and threshing section, having a special rasp bar whose character changes along its length to increasingly attenuate the mat of crop material as it approaches the threshing section. It is also known, in a separator having a generally cylindrical rotor, to provide concave relief at the threshing section inlet. In the latter, extra radial clearance between rotor and concave is provided over a significant length of rotor at the threshing zone inlet by relieving the concave. However, this approach sets up a diameter-reducing constriction or step within the threshing zone to surmount which the mat of material must be further reduced in thickness in a radially inward direction, that is to say against the action of centrifugal force. The rotor is required to force crop material radially inwards over the fixed step.